Air cylinders for pneumatic tool have a cylinder chamber, in which a rotor is mounted. The rotor has a plurality of vanes mounted on a circumferential surface thereof, such that outer edges of the vanes are in close contact with an inner wall surface of the cylinder chamber. High-pressure air is guided into the cylinder chamber via an air inlet on the air cylinder to drive the rotor to rotate, and then discharged as exhaust air via an exhaust hole on the air cylinder.
FIGS. 1 and 2 show two conventional cylinder bodies 10, 20 for air cylinders. As shown, air inlets 12, 22 and exhaust holes 14, 24 all are provided on the cylinder bodies 10, 20 to communicate with the cylinder chamber 16, 26. To form the air inlet and the exhaust hole on a circumferential wall of the cylinder body, the cylinder body must be machined several times in a non-continuous manner. That is, the cylinder bodies 10, 20 must be turned to form the cylinder chambers 16, 26, and then machined to form the air inlets 12, 22 and the exhaust holes 14, 24.
Since the forming of the cylinder chamber, the air inlet, and the exhaust hole on the cylinder body necessitates different and non-continuous processing steps, it is uneasy to produce the cylinder body and the manufacturing cost thereof is high.
Moreover, the different non-continuous processing steps for forming the cylinder body produce height differences on inner wall surface of the cylinder chamber 16, 26, resulting in a stepped, unsmooth, and burr-containing inner wall surface of the cylinder chamber. When the rotor rotates, the vanes thereof tend to be quickly worn off at outer edges by the unsmooth surface of the cylinder chamber, and therefore have a shortened service life and require frequent replacement.